1. Field of the Invention
The present invention relates to a motor control device which controls a motor for driving a carriage of an image forming apparatus, such as an inkjet printer or the like, to a motor control method, and to a program.
2. Background Art
In the related art, an inkjet printer has a carriage that can reciprocate along a guide shaft in order to mount a recording head. The carriage is driven by means of a motor, such as a direct current (DC) motor or the like.
The DC motor has a structural problem in that, even when an input current value or voltage value is constant, torque is not uniform during the rotation of a motor shaft and thus a cyclic change in torque, which is a so-called cogging cycle, occurs. For this reason, the rotational velocity of the DC motor is pulsated periodically. As a result, the driving velocity of the carriage to be driven by the DC motor is also pulsated periodically.
When the driving velocity becomes high due to the pulsation of the driving velocity of the carriage, ink is ejected from the recording head on a recording medium at a large interval, which causes a thin color in a corresponding portion. On the contrary, when the driving velocity of the carriage becomes low, ink is ejected from the recording head on the recording medium at a small interval, which causes a thick color in a corresponding portion.
Accordingly, if the driving velocity of the carriage is pulsated, as for regions where colors must be recorded with the same concentration, thick color regions and thin color regions alternately appear, which results in a stripe shape.
Therefore, a method has been suggested in which the pulsation in the driving velocity of the carriage is reduced by overlapping a cyclic signal, which has the same cycle as the cogging cycle but has a phase opposite to that of the cogging cycle, and the driving signal of the DC motor (See JP-A-11-18475) each other. For example, at a timing at which torque of the DC motor is increased by the cogging cycle, the output of the driving signal is reduced by the overlap cyclic signal to suppress the driving velocity of the carriage. On the contrary, at a timing at which torque of the DC motor is decreased, the driving signal is increased by the overlap cyclic signal to increase the driving velocity of the carriage. Therefore, the driving velocity of the carriage becomes constant.